Trehalose, the alpha-1,1 linked disaccharide of glucose, serves as a major storage form of carbohydrate in the tissues of Ascaris. This laboratory is currently investigating the synthesis and degredation of this disaccharide. In Ascaris, UDP-glucose appears to serve as an effective glucosyl donor and glucose-6-phosphate as an effective glucosyl acceptor from the synthesis of trehalose phosphate. In crude extracts of reproductive tissue ATP may act as a modulator. TDP-glucose may also serve as a glucosyl donor, being more active than UDP-glucose in crude homogenates and less active in preparations devoid of glycogen synthetase activity. Trehalase, the enzyme involved in the degredation of trehalose, has been detected in all the tissues of Ascaris. The specific activity of the enzyme in muscle is two to three times greater than that found in the other tissues. Muscle has been used as the source of enzyme for experiments designed to characterize trehalase. Trehalase activity in this tissue can be separated into two fractions by centrifugation of a crude homogenate at 15,000 x g for 20 minutes. Approximately 80 percent of the enzymatic activity is found in pellet and 20 percent in the supernatant. The soluble enzyme has been subjected to partial purification and characterization by ammonium sulfate fractionation DEAE cellulose chromatography and gel filtration. Maximum enzymatic activity is obtained at pH 6. The enzyme does not require nor is its activity stimulated by divalent cations. The apparent km for trehalose is 3.4 x 10 to the minus 4th power M. The enzyme appears to be specific for trehalose when tested with a wide variety of disaccharide substrates. The antibiotic trehalosamine acts as a competative inhibitor of enzymatic activity.